Controlled struvite crystallization is regarded as a promising route to phosphorus recovery from wastewaters, and has been the topic of extensive research in the last two decades. Most studies made great efforts to elevate the quantity of struvite recovered from various wastewaters, but little attention has been focused on the struvite quality which affects the agronomic response. The improvement of struvite quality can raise its value in fertilizer markets and improve the economical sustainability of struvite crystallization technology. In this study, we report a facile method for the synthesis of struvite nanowires by regulating NaCl concentration and initial pH (pH i ) in synthetic wastewater. The identification and characterization of the synthesized products were done using X-ray powder diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and Zeta potential Analyzer. Our results reveal that both NaCl concentration and pH i play important roles on the phase composition and morphology of products in the crystallization system. In particular, a mass of struvite nanowires with high yield can be obtained at NaCl concentration ranging from 3.5 to 4.5 wt % at pH i 11.0, and the mechanism for the formation of struvite nanowires was systematically investigated. As struvite has been regarded as a fertilizer, struvite nanowires can potentially act as a new kind of nanofertilizer with higher efficiency.
Clays are widely used as sorbents for heavy metals due to their high specific surface areas, low cost, and ubiquitous occurrence in most soil and sediment environments. However, the low loading capacity for heavy metals is one of their inherent limitations. In this work, a novel SiO2–Mg(OH)2 nanocomposite was successfully prepared via sequential acid–base modification of raw sepiolite. The structural characteristics of the resulting modified samples were characterized by a wide range of techniques including field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and nitrogen physisorption analysis. The results show that a hierarchical nanocomposite constructed by loading the Mg(OH)2 nanosheets onto amorphous SiO2 nanotubes can be successfully prepared, and the nanocomposite has a high surface area (377.3 m2/g) and pore volume (0.96 cm3/g). Batch removal experiments indicate that the nanocomposite exhibits high removal efficiency toward Gd(III), Pb(II), and Cd(II), and their removal capacities were greatly enhanced in comparison with raw sepiolite, due to the synergistic effect of the different components in the hierarchical nanocomposite. This work can provide a novel route toward a hierarchical nanocomposite by using clay minerals as raw material. Taking into account the simplicity of the fabrication route and the high loading capacities for heavy metals, the developed nanocomposite also has great potential applications in water treatment.
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